Danfoss VLT FC51 Design Manual page 49

How to Install
6.8.2 Motor Cables
See chapter 9 Specifications for maximum dimensioning of
motor cable cross-section and length.
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Use a screened/armoured motor cable to comply
with EMC emission specifications.
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Keep the motor cable as short as possible to
reduce the noise level and leakage currents.
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Connect the motor cable screen to both the de-
coupling plate of the frequency converter and to
the metal cabinet of the motor.
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Make the screen connections with the largest
possible surface area (cable clamp). This is done
by using the supplied installation devices in the
frequency converter.
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Avoid mounting with twisted screen ends
(pigtails), which spoils high frequency screening
effects.
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If it is necessary to split the screen to install a
motor isolator or motor relay, the screen must be
continued with the lowest possible HF
impedance.
6.8.3 Electrical Installation of Motor Cables
Screening of cables
Avoid installation with twisted screen ends (pigtails). They
spoil the screening effect at higher frequencies.
If it is necessary to break the screen to install a motor
isolator or motor contactor, the screen must be continued
at the lowest possible HF impedance.
Cable length and cross-section
The frequency converter has been tested with a given
length of cable and a given cross-section of that cable. If
the cross-section is increased, the cable capacitance - and
thus the leakage current - may increase, and the cable
length must be reduced correspondingly.
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VLT Micro Drive FC 51 Design Guide
Switching frequency
When frequency converters are used together with Sine-
wave filters to reduce the acoustic noise from a motor, the
switching frequency must be set according to the Sine-
wave filter instruction in 14-01 Switching Frequency.
Aluminium conductors
Aluminium conductors are not recommended. Terminals
can accept aluminium conductors but the conductor
surface has to be clean and the oxidation must be
removed and sealed by neutral acid free Vaseline grease
before the conductor is connected.
Furthermore, the terminal screw must be retightened after
2 days due to the softness of the aluminium. It is crucial to
keep the connection a gas tight joint, otherwise the
aluminium surface oxidises again.
6.8.4 EMC-Correct Electrical Installation
General points to be observed to ensure EMC-correct
electrical installation.
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MG02K302 - Rev. 2013-12-03
Use only screened/armoured motor cables and
screened/armoured control cables.
Connect the screen to earth at both ends.
Avoid installation with twisted screen ends
(pigtails), since this ruins the screening effect at
high frequencies. Use the cable clamps provided
instead.
It is important to ensure good electrical contact
from the installation plate through the installation
screws to the metal cabinet of the frequency
converter.
Use starwashers and galvanically conductive
installation plates.
Do not use unscreened/unarmoured motor cables
in the installation cabinets.
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